Modified hot runner systems for injection blow molding

ABSTRACT

An injection blow molding method for making a container having the steps of injecting a molten crystallizable polymer in a preform mold via a hot runner system and biaxially stretching the preform by blowing to form a container. The method further having the step to selectively modify the flow path of the molten crystallizable polymer within the hot runner system.

FIELD OF THE INVENTION

The present invention relates in general to new developments ofthermoplastic preforms in particular of the type used for blow moldingcontainers, and more particularly to preforms having a crystallized neckfor resistance to deformation at elevated temperatures. It also relatesto a method for producing said containers and, in particular, topreforms used for their production, as well as a method for producingsaid preforms.

BACKGROUND OF THE INVENTION

The use of plastic containers as a replacement for glass or metalcontainers in the packaging of beverages has become increasinglypopular. Several types of plastics have been used, ranging fromaliphatic and aromatic polyolefins (polyethylene, polypropylene,polystyrene) over halogenated polymers (polyvinyl chloride,polyvinylidene chloride) and aliphatic polyamides (nylons) to aromaticpolyesters. As far as the rigid food packaging sector is concerned,polyethylene terephthalate (PET), an aromatic polyester, is by far themost widely used resin. This choice is driven by its unique materialproperties, combining amongst others shatter resistance, lightweight,high mechanical strength, transparency, recyclability, . . . . Beverageapplications, both for carbonated and non-carbonated products,constitute the single largest application area for PET containers. MostPET containers are made by stretch blow molding of preforms which havebeen made by processes including injection molding. In somecircumstances, it is preferred that the preform resin is amorphous oronly slightly semi-crystalline in nature, as this allows for stretchblow molding. Highly crystalline preforms generally are difficult, ifnot impossible to stretch blow mold.

With plastic materials (like PET) being derived from oil, the ongoingincreases in resin, oil and energy pricing has created significantpressure on package owners to reduce the total cost of ownership oftheir plastic packaging mix. This in turn drives focus on findingsolutions which enable to further reduce the wall thickness of theseplastic (like PET) containers (light-weighting) whilst maintaining theinherent overall performance characteristics and design flexibility. Italso challenges the plastic material converting industry to increase theoutput of its plastic material converting platforms, on processes likeinjection and stretch blow molding. The combination of reduced materialutilization and increased production manufacturing output reduces thetotal cost of ownership for both preforms and containers.

At the same time, in some specific end market applications, increasedperformance specifications are requested on parameters including thermalstability, barrier performances and mechanical rigidity. Such a specificend market application requesting increased performance specificationsfor PET containers includes hot-fill containers, which must withstandfilling with hot liquid products without significant deformation,followed by sealing and a cooling process which creates a vacuum in thecontainer, due to the volume contraction of the hot filled liquid.

A particular problem associated with these hot-fill containers concernsthe thermal stability of both the body, but especially the neck finishof the container throughout the hot filling process, because increase intemperature during the process induces molecular relaxation andshrinkage in the container material. The higher the crystallinity of thecontainer, the more the container is resistant to said relaxation. Whenan essentially amorphous or only slightly semi-crystalline preform isconverted into a container by the stretch blow molding process, theprocess conditions determine the amount of crystallinity that is inducedin the different container parts. Unless special precautions are takenand/or additional process steps are included, the neck finish, beingclamped and restricted from stretching, will receive almost no increasein crystallinity. Any increase obtained will always be negligible incomparison to the increase induced in the stretched main body. Anycontainer part made entirely of amorphous or only slightlysemi-crystalline PET may not have enough dimensional stability during astandard hot-fill process to resist the relaxation process and hencemeet the specifications required when using standard threaded closures.

Unacceptable volume shrinkage of the container and/or especially of theneck area may create leaks between the neck and closure, thus increasingexposure to micro-organisms, whilst increasing gas ingress and/oregress. This can lead to non-specification compliant quality issues and,in case of food applications, to potentially consumer hazardoussituations when pathological micro-organisms are able to grow inside thepacked food matrix.

In these circumstances, a container comprising increased amounts ofcrystalline PET, especially in the neck finish, would be preferred, asit would hold its shape during hot-fill processes.

Another application in which plastic containers are subjected toelevated temperatures, include pasteurisable containers which, afterfilling and sealing, are then exposed to an elevated temperature profilefor a defined time period. Throughout the pasteurization process, thesealed container must have dimensional stability so as to remain tightand within the specified volume tolerance.

Yet another high-temperature application is the use of plasticreturnable and refillable containers for both carbonated andnon-carbonated beverages, whereby the container must withstand wash andreuse cycles. Such containers are filled with a carbonated ornon-carbonated beverage, sold to the consumer, returned empty, andwashed in a hot, potentially caustic solution prior to refilling. Theserepeated cycles of thermal exposure make it difficult to maintain theoverall shape, appearance and threaded neck finish within the tolerancesrequired to ensure adequate functionality and/or general consumeracceptance.

A number of methods have been proposed to address said problems ofelevated temperature impact on plastic containers throughout theirfilling or use cycle, thereby ensuring that the required specificationsfor volume shrinkage, shape retention, neck softening and others aremet.

One such method consists of adding an additional manufacturing step thatexposes the neck finish and/or body part of the preform or container toa heating element in order to thermally crystallize the neck finishand/or body part of the preform or container. However, the requiredcapital investments, the increased manufacturing processing time andcosts for specific materials and/or auxiliaries lead to an increasedoverall cost of ownership and increased total product cost. Aspreviously stated, the overall cost of producing a container is veryimportant and needs to be tightly controlled because of competitivemarket and business pressures.

Alternative methods of strengthening the neck finish involvecrystallizing select portions of the neck finish, such as the topsealing surface and flange. Again, this requires an additional heatingstep and increased processing time.

Another alternative is to use a high glass transition temperaturematerial in one or more layers of the neck finish. Generally, thisinvolves more complex preform injection molding procedures to achievethe necessary layered structure in the finish.

Another alternative method includes specific container design and designfeatures such as to compensate for the developed vacuum through thehot-fill process.

A particular performance characteristic associated and critical tocarbonated beverage containers, include barrier performance i.e. thecontrol of gas ingress and/or egress. To conserve the taste of thebeverage and hence increase the shelf life of the product, it isessential that the gas mixture in the container remains unchanged for aslong as possible after the filling process. Different methods are beingused nowadays to enhance the barrier properties of the container walls,including passive methods (co-extrusion multilayer approaches, coatingapplications, nanotechnology) and active methods (oxygen scavengerincorporation) and combinations thereof. All these methods significantlyincrease the cost of ownership.

With respect to mechanical properties, commercial articles in generalmade out of polyesters and more specifically out of PET depend primarilyon some degree of orientation induced during the manufacturing processesto enhance the mechanical properties.

The degree of molecular orientation and the physical properties of theresulting oriented article are governed o.a. by the strain rate appliedduring processing, by the stretch ratio, by the molecular weight of theresin and by the temperature at which the orientation takes place.Bi-axial orientation during stretch blow molding when transforming apreform into a container leads to strain induced crystallization. Thisin turn improves mechanical strength and barrier properties. The amountof crystallinity reached and the crystal shape depend on the strain rateand the stretching temperature. State of the art production methods areoptimized to enhance the mechanical strength by stretching the amorphouspreform to maximal strength within the limits of the materialcharacteristics. Typical average applied stretch ratios amount to up to4.5 in the circumferential direction and up to 3.2 in the axialdirection. Exceeding these limits and entering ranges of too highstretch ratios lead to the creation of micro voids and prematurecontainer failure.

A particular problem when blow molding remains generating enhancedmechanical strength in the neck finish and in the bottom portion of thecontainer in light of the negligible respectively low stretch ratios inthese specific areas.

Especially in the case of containers intended for filling withcarbonated soft drinks this local reduction in strength leads to moresevere container deformation and consequently to a reduction ofdissolved carbon dioxide in the soft drink and to a decreased shelflife. To alleviate the inherent weakness of these particular areasrecourse is taken to preforms exhibiting significant higher wallthicknesses in neck finish and bottom area.

Another widely used method to capitalize on the induced crystallinityand to extend it into less oriented areas is the process calledheat-setting, in which the transformation from amorphous preform tocrystalline container is preformed at high temperature for ratherprolonged exposure cycle times.

A particular limitation, state of the art production methods sufferfrom, stems from the preheating prior to stretch blow molding thecontainer and more specifically to the heat history heat-set containersare subjected to.

In the heat-set process the preform and resulting container are exposedto significantly higher temperatures then is the case for so-calledcold-drawn bottles, as e.g. used for water and carbonated soft drinks. Atypical preform reheat temperature for a heat-set container amounts to130° C. versus 90-100° C. for cold-drawn containers.

Following the preform is stretch blown in a heated container blow moldwhere only the inner container wall is air cooled.

Typical heat-set container mold temperatures are in the range of 160° C.In contrast a cold-drawn container is blown in a mold kept at around20°.

This thermal treatment destroys most of the stretch induced orientationas relaxation processes have ample time to develop. As a consequence theresulting heat-set container looses a substantial amount of mechanicalstrength. The ultimate mechanical strength reached in the heat-setbottle is achieved predominately by additional crystallization throughthe prolonged thermal treatment.

Overall the resulting heat-set container strength is lower than that ofa typical cold-drawn container.

Therefore heat-set containers necessitate higher material demand, longerprocess cycle times and the application of more energy compared tocold-drawn containers.

From the above it is clear that it would be desirable to provide amethod of manufacturing a preform made out of crystallizable polymersfor a container having a neck finish which resists deformation,particularly at elevated temperatures, characterized in that it isproduced within the standard processing time frame and/or limitedextensions thereof.

It is equally clear that it would be desirable to provide a method ofmanufacturing a preform made out of crystallizable polymers for acontainer having, at optimized wall thicknesses, equal or superior endperformance properties including, amongst others, gas permeationresistance and mechanical strength.

According to a first embodiment of the present invention, the presentinvention is directed to a method for making out of crystallizablepolymers an article in general, or more specifically a preform andresulting stretch blow molded container, providing equal or superior endperformance characteristics. Said method includes hot runner systemmodifications, thereby inducing new structures both at the level ofpreform and/or container.

Another embodiment of the present invention provides a method andapparatus for the cost-effective manufacture of such articles ingeneral, specifically injection molded preforms and stretch blow moldedcontainers.

SUMMARY OF THE INVENTION

The present invention describes a method for producing preforms andcontainers made out of crystallizable polymers, in particular of thetype used for stretch blow molded containers, and more particularlypreforms and containers with optimized wall thickness, yet superioroverall performance characteristics, including enhanced resistance tothermal deformation both in the body and especially the neck finish, gaspermeability resistance and mechanical strength.

BRIEF DESCRIPTION OF THE DRAWINGS

Examples of different embodiments of the invention will now be explainedin more detail with reference to the drawings, wherein:

FIG. 1 illustrates an injection system that uses the specially designedinserts, i.e., hot runner modifications, according to the presentdisclosure;

FIG. 2 illustrates one embodiment of the hot runner modification of theinjection system;

FIG. 3 illustrates a second embodiment of the hot runner modification ofthe injection system;

FIG. 4 illustrates a third embodiment of the hot runner modification ofthe injection system;

FIG. 5 illustrates a fourth embodiment of the hot runner modification ofthe injection system;

FIG. 6 illustrates a fifth embodiment of the hot runner modification ofthe injection system;

FIG. 7 illustrates a sixth embodiment of the hot runner modification ofthe injection system;

FIG. 8 illustrates a seventh embodiment of the hot runner modificationof the injection system;

FIG. 9 illustrates an eighth embodiment of the hot runner modificationof the injection system;

FIG. 10 a-10 b is a schematic representation of the regular or irregularsequence of variations in molecular pre-alignment/orientation inaccordance with the hot runner modification of the injection system.

DETAILED DESCRIPTION

In the description, the following definitions have been applied for:

-   -   “Crystallizable polymer” means a polymer exhibiting both        amorphous and crystalline regions when cooled to an equilibrium        state below the melting point.    -   “Crystallinity” means the volume fraction of the crystallizable        polymer that is packed in the crystalline state. This volume        fraction is calculated as P−P_(a)/P_(c)P_(a) where P is the        density of the tested material; P_(a) is the density of pure        amorphous material (e.g. PET: 1.333 g/cm³); and P_(c) is the        density of pure crystalline material (e.g. PET: 1.455 g/cm³).    -   “Pre-stratified structure” means the regular or irregular        sequence of variations in molecular pre-alignment/orientation        and/or crystallinity between different locations of the        cross-section of the preform. “Stratified structure” means the        regular or irregular sequence of variations in molecular        pre-alignment/orientation and crystallinity between different        locations of the cross-section of the container.

As stated hereinabove, while a preform with reduced crystallinity levelis preferred for stretch blow molding, a container having a higherdegree of crystallinity is preferred for its overall enhanced endperformance characteristics, including better thermal stability in caseof exposure to elevated temperatures during its filling or usage cycle,increased gas permeation resistance and higher mechanical strength.

Unless special precautions are taken during the injection moldingprocess (e.g. quenching techniques), injection molded articles ingeneral, specifically preforms manufactured out of crystallizablepolymers, consist of crystalline regions, where molecules are packedregularly and densely with strong short-range inter-chain interactionsholding them together, and non-crystalline or amorphous regions, wheremolecular packing is either irregular and less dense and/or to somedegree regular but even less dense than the irregular amorphousfraction.

In the crystalline regions, deformation (e.g. stretching by stretch blowmolding) is much more difficult to achieve due to the strong short-rangemolecular inter-chain locking mechanism mentioned. Consequently,increasing the proportion of crystalline regions, that is, the increasein crystallinity, results in reduced stretch blowing capabilities.

In order to facilitate the stretch blow molding process, that transformsthe predominantly amorphous preform through the intermediate step ofamorphous chains orientation into a three-dimensional crystalline thusstrong container, it is therefore state of the art practice to quenchthe polymer melt in the injection cavity so as to prevent thecrystallization in the preform. As also the neck finish is quenched, itis as void of crystallinity as the body part. Contrary to the body parthowever, the neck finish, being clamped and restricted from heat-up andstretching, cannot crystallize during the stretch blow molding step.

The end result of the state of the art process is therefore a containerwith oriented crystalline body and less or non-oriented amorphous neckfinish, which leads to the neck softening problems and the currentlyused workarounds, as described hereinabove.

The underlying governing physical principles are as follows:

When a polymer melt of a crystallizable polymer is cooled down rapidly,i.e. quenched, the material vitrifies before the onset ofcrystallization can take place. The vitrification process results in adrastic restriction of the macromolecular segmental mobility, in otherwords the vitrified macromolecules can no longer arrange themselvesefficiently so as to start building crystallites. The vitrificationprocess also locks in any pre-alignment/orientation of themacromolecules that may have been present in the polymer melt at themoment of quenching. The vitrified material is therefore amorphous innature.

When the vitrified amorphous material is heated up in preparation forthe stretch blow molding process, the locked inpre-alignment/orientation is released as soon as the vitrificationtemperature is reached. Since the heating cycle is very slow on amolecular time scale, relaxation processes can become active and theanisotropy that might have been locked in during the prior vitrificationof the polymer melt may disappear again, leaving the material to agreater extent isotropic in nature.

Next, the heated material is biaxially stretched in the stretch blowmolding process. Dependent on the temperature at which the stretch blowmolding takes place, onset and rate of induced crystallization may vary.The period of time in which the preform is stretched to a containerhowever is sufficiently long on a molecular time scale level to warrantcrystallization, as can be appreciated by those skilled in the art. Inaddition, it is known to those skilled in the art that the rate ofcrystallization induced by the stretching process is much higher thanany crystallization rate reached using the temperature parameter only.

Translating the above to the state of the art practice of manufacturingcontainers by the injection and stretch blow molding process, it hasbecome clear why the neck finish exhibits less thermal stability thanthe body part of the container at the end of the stretching operation:

The body part was quenched to an amorphous state during the injectionmolding process, was heated and stretch blow molded hereby becomingcrystalline in nature as desired.

The neck finish was quenched to an amorphous state during the injectionmolding process, was left cold and restricted from stretching beforerespectively during the stretch blow molding process, and thereforeremained amorphous in nature and void of any increase in crystallinity.

In order to increase the thermal stability of the neck finish, it needsto become crystalline in nature. Modifications and additions to themanufacturing process have been proposed as described earlier on. All ofthese suffer from being slow and hence add valuable and costly time tothe manufacturing process. The reason for this is to be found in thesecond physical phenomenon mentioned: the difference in crystallizationrate between heat-induced crystallization and mechanically inducedcrystallization, be this by shear, flow, stretching strain or the like.

In accordance with the present invention, it has now been surprisinglyfound that the effect of induced pre-alignment/orientation ofmacromolecules in the polymer melt may be synergistic with the effect ofcrystallinity, in an accelerated way. By use of the both effects,articles in general, or more specifically preforms and stretch blowmolded articles, specifically containers, thereof can now be obtained,having superior properties that have never been attained by conventionalmethods described in the prior art.

According to the present invention, both the crystallinity and thepre-alignment/orientation of the macromolecules in the polymer meltgovern the properties of the articles in general, specifically preformsand stretch blow molded articles, specifically containers, made out ofcrystallizable polymers.

The current invention combines the effect of pre-alignment/orientationof the macromolecules in the polymer melt with the well-knowncrystallinity effect in order to achieve the synergistic performanceenhancement in the article in general, more particularly the preformand/or container.

By means of controlled local friction/shear through the introduction ofmodifications inside the hot runner system, the synergistic combinationunderlying the present invention allows introducing orientationgradients and hence stratification over the wall section of the articlesmade out of crystallizable polymers, including the preform and theresulting stretch blown container.

The mechanism of controlled local friction/shear andsynergistic/cumulative combination of pre-alignment/orientation andcrystallization of the crystallizable polymer in turn allows creating apre- and stratified structure across the manufactured end products, likepreforms and containers, leading to end articles having high thermalresistance, gas permeation resistance and mechanical strength.

By creating said orientation gradients and pre- and stratifiedstructures, articles like preforms can be made that will result in equalor superior end performance characteristics in the containersmanufactured thereof at optimized wall thickness and/or retain thenecessary dimensions in the neck finish and/or body part when the finalcontainer is being subjected to elevated temperatures during its fillingor usage cycle.

By controlling the local friction/shear and resultingpre-alignment/orientation of the macromolecules of the crystallizablepolymer within the injection process, the mechanisms, positions andrates of movement of the molecules thereof are regulated both in thepolymer melt matrix and in the final wall matrix in the articlesmanufactured, like in the preform and the stretch blow molded articlethereof.

More practically, in the method according to the present invention, theamount of pre-alignment/orientation of the macromolecules of thecrystallizable polymer in the polymer melt and the resultant molecularorientation and orientation gradients obtained in the article in generalare regulated primarily within the hot runner system. Thenature—semi-crystalline or amorphous—and the distribution of this natureacross selected regions of the article in general, specifically thepreform after the injection molding process, is regulated primarilywithin the preform cavity of the injection process.

As stated above and in accordance with the present invention, thepre-alignment/orientation of the macromolecules is induced bycontrolling the local friction/shear within the injection process.

To generally align macromolecules that facilitate creation of thedesired orientation gradients and pre- and stratified structures in thearticle in general, specifically in the preform, the polymer meltmacromolecules are oriented in the hot runner of the injection system bycontrolling the locally applied friction/shear. This can, amongstothers, be achieved by passing the molten polymer through speciallydesigned internal hot runner modifications such as profiling of the busand/or needle or placing inserts within the hot runner system. Ifneeded, this can be combined with high injection pressure or repetitivecompression and decompression cycles.

In contrast with hot runners for state of the art injection moldingprocesses whereby these hot runners are typically designed to avoidfriction/shear when the polymer flows through the hot runner, thepresent invention utilizes the control of locally applied friction/shearin the said hot runner as means to introduce preferredpre-alignment/orientation of the macromolecules. Additionalfriction/shear can also be induced at the entrance to the preformcavity.

The basic principle behind this feature is the fact that the flow pathor flow channel, through which the selected materials will flow, isbeing modified from a cross-sectional point-of-view and in relation toits length. The hot runner construction is modified in a manner to forcethe polymer melt into pre-alignment/orientation.

The variations of said modifications of hot runner construction includeconfigurations of the hot runner which can be obtained by applying someof the following, non-exhaustive or non-limitative adjustments, eitherused alone or in combination:

-   -   i) changing the diameter of the flow channel,    -   ii) introducing Venturi restrictions for the melt flow, followed        by channels of defined length producing subsequent expansion of        the flow,    -   iii) appropriate sloping of said restrictions or expansions,

Practically, without being limitative or exhaustive, this can berealized by profiling of the needle and/or the outer housing of the hotrunner (bus) and/or introducing inserts (e.g. geometrical configurationsselected from one or more of concentric tubes, star wheels, or zoneshaving diameter variations), at selected positions in the hot runner.

Additional friction/shear at the entrance to the preform cavity can beachieved by reducing the orifice hole inside the hot runner.

The final flow channels obtained in the hot runner can be very diversein design and can be symmetrical or non-symmetrical as required toachieve the desired final stratified configuration of the container.

Without wishing to be bound by any theory, the physical and chemicalphenomena that form the basis for the invention will now be described:

It is common knowledge that quenching of isotropic polymer melts leadsto vitrification of the macromolecules at a temperature, characteristicfor that particular polymer, the so-called glass transition temperature.Below the glass transition temperature, the macromolecular segmentalmobility is drastically restricted, as the macromolecules are “frozenin”. Above the glass transition temperature the macromolecular segmentalmobility increases steadily with increase of temperature. As the amountof macromolecular segmental mobility increases, matrix randomization,known as relaxation, becomes more and more predominant, leadingultimately to an isotropic melt.

It is known by those skilled in the art that anisotropic, i.e.pre-aligned/oriented, polymer melts behave quite differently uponquenching/cooling. Dependent on the degree of pre-alignment/orientation,the vitrification process takes place at temperatures exceeding thecharacteristic glass transition temperature of the polymer and thevitrification leads to a more dense amorphous structure.

Therefore, when a polymer melt featuring different degrees ofpre-alignment/orientation, such as a stratified polymer melt, isquenched, those parts exhibiting the highest degree ofpre-alignment/orientation will vitrify first, i.e. at the highesttemperature, whereas those parts exhibiting no pre-alignment/orientationwill vitrify at the glass transition temperature. Parts featuringintermediate degrees of pre-alignment/orientation will vitrify atintermediate temperatures. The result is a highly anisotropic amorphouspolymer glass, featuring regions with molecular packing ranging fromfully random, i.e. irregular, to structured, i.e. pre-aligned/oriented.These orientation gradients translate into density gradients, with thestructured regions featuring a higher density.

Upon reheating the cooled vitrified polymer matrix, onset ofmacromolecular segmental mobility will occur in the reversed order, i.e.the lower the degree of pre-alignment/orientation in the glassy state,the earlier (i.e. at lower temperature) the onset of macromolecularsegmental mobility (which as stated before leads to randomization intoan isotropic structure, i.e. relaxation) once the glass transitiontemperature is crossed in the heat-up process.

From the above, it is clear that the pre-alignment/orientation frozen ininto the glassy state during the first quenching process is retainedafter heating up such a polymer matrix above its glass transitiontemperature. Dependent on the ultimate temperature reached in theheating cycle, some regions in the polymer matrix will remain vitrified,namely those with increasing degrees of pre-alignment/orientation thatvitrified at temperatures exceeding the one reached in the heat-upcycle.

These phenomena thus enable to maintain the during the injection processin the preform induced pre- and stratified structure during thepreheating prior to stretch blow molding and then to transform thestratified amorphous structure into a stratified crystalline structurein the stretch blow molding process.

Variations in the cooling/quenching rate in the injection cavity enablestreamlining the nature—amorphous or semi-crystalline—of the vitrifiedpolymer melt.

Whereas fast quenching locks in pre-alignment/orientation in the glassyvitrified state, reduced rates of cooling/quenching allow forcompetition to progressively develop between the vitrification andcrystallization processes.

As it is known for those skilled in the art thatpre-alignment/orientation accelerates the rate of crystallizationdramatically with respect to the heat induced crystallization,relatively small differences in cooling rate can cause significantdifferences in the nature of the cooled polymer matrix.

Contrary to the additional heating steps utilized in the current stateof the art processing as described earlier on, the crystallization ofthe strongly pre-aligned/oriented polymer fraction in the pre- andstratified structure occurs on a much smaller time scale and well withinthe time frame typical for state of the art preform injection cycletimes and/or limited extensions thereof.

Above phenomena allow for the introduction of the regular or irregularsequence of variations in molecular pre-alignment/orientation (see FIGS.10A and 10B) and/or crystallinity between different locations of thecross-section of the preform.

Adjusting the cooling/quenching rate in the injection cavityappropriately (i.e. time and location wise) will facilitatemanufacturing in the injection molding process a preform, havingsubstantial pre-stratified structure. Such a preform will be transformedinto a crystalline container during the sole stretch blow moldingprocess with no need for additional heating or processing steps tostrengthen the neck finish.

Above phenomena equally allow for the introduction of the regular orirregular sequence of variations in molecular pre-alignment/orientationand crystallinity between different locations of the cross-section ofthe container.

By adjusting the cooling/quenching rate in the injection cavityappropriately (i.e. time and location wise), it will facilitatemanufacturing in the injection molding process of a container havingsubstantial stratified structure in the body part. Such a container willnot need additional heating or processing steps to strengthen the neckfinish.

The different levels of cooling are preferably maintained by thermalinsulation of the regions requiring lower cooling rates. This thermalinsulation can be accomplished e.g. by utilizing a combination of lowand high thermal conduct materials as inserts.

The processes according to the present invention preferably accomplishthe making of a preform within the preferred cycle times, and/or limitedextensions thereof, for standard PET preforms of similar size, designand weight by standard methods currently used in preform production.Said processes are enabled by tooling design and process techniques toallow for the simultaneous generation of orientation gradients anddifferent degrees of crystallinity in particular locations on thepreform.

The cooling of the mold in preform regions for which it is preferredthat the material be generally amorphous or semi-crystalline, isaccomplished by chilled fluid circulating through selected regions ofthe mold cavity and core.

Bearing in mind the consideration about the mechanism of the inventiondescribed hitherto, it will be readily understood that the injectionprocess conditions can be optimized to the well specified range in orderto make the articles in general, more particularly the preforms andresulting stretch blow molded containers of the present invention.

The present invention can be applied to various crystallizable polymersto manufacture articles in general, specifically preforms and containersthrough processes including injection and stretch blow molding.

The preform and container may be made solely of PET or anothercrystallizable polymer, preferably but not exclusively an aromatic oraliphatic polyester, a blend of aromatic or aliphatic polyesters, anaromatic or aliphatic polyester copolymer or any combination thereof.

Preferred examples include polyethylene terephthalate (PET),polyethylene naphthalate (PEN), polytrimethylene terephthalate (PTT),polytrimethylene naphthalate (PTN), polylactic acid (PLLA) andcopolymers and blends thereof.

The preforms made out of crystallizable polymers are preferablymonolayer i.e. comprised of a single layer of a base material, or theymay be multilayer, including, but not limited to, those which comprise acombination of a base material and a barrier material. The material ineach of these layers may be a single type of a crystallizable polymer orit may be a blend of crystallizable polymers.

In accordance with the present invention, it has also been found thatthe pre-alignment/orientation of the amorphous macromolecules can befurther positively influenced through the utilization of acrystallizable polymer with a higher molecular weight, as onceorientation has been achieved, pre-aligned macromolecules from acrystallizable polymer with a higher molecular weight exhibit a higherresistance to relaxation, herewith retaining the orientation over alonger time period.

It is clear that a method according to the present invention may haveconvincing advantages compared to prior art methods. In specific, forarticles in general, or more particularly preforms and containers madeout of crystallizable polymers by manufacturing processes includinginjection and stretch blow molding, through the achievement ofstratification in the body and the neck finish during the injectionmolding step, the desired end benefits can be obtained including,amongst others, minimized dimensional variations in the neck finishunder elevated temperatures due to the higher average level ofcrystallinity reached in the neck finish, equal or better gas permeationresistance and higher mechanical strength.

Furthermore, by the process of the present invention, the prior artsteps of exposure to thermal heating elements, crystallization of selectportions, utilization of high glass transition temperature materials incombination with more complex injection molding processes and/or theprocesses including post-mold thermal crystallization can be eliminatedand the manufacturing of the said preforms and containers occurs withinthe usual standard manufacturing time frame and/or limited extensionsthereof.

In particular for articles in general made by processes includinginjection and/or stretch blow molding operations, and more particularlyfor preforms and containers made out of crystallizable polymers, thepresent invention can lead to a further reduction of the article's wallthickness given the increased mechanical strength obtained from thecreation of the stratification across the article wall. In turn thereduction of the wall thickness can create a substantial increase in theoperational output of the injection and/or stretch blow molding process.These benefits combined allow for a further reduction of the total costof ownership of the produced articles in general, specifically preformsand containers made out of crystallizable polymers.

Having the increased mechanical strength of the finally blown containeralso allows for the absorption of the vacuum upon cooling of the liquidwhich enables the making of containers having a simpler design andgeometry compared to conventional containers having vacuum panels and/orother specially designed features in the bottle geometry allowing thevacuum absorption.

The above advantages make the articles of the present invention verysuitable for high specialty applications including hot-fill applicationsand diverse carbonated and/or non-carbonated beverage applications.

EXAMPLES 1. Injection System (FIG. 1)

-   -   a. A commercially available grade of a crystallizable polymer,        being PET, is taken within a classical IV range of 0.78-0.82,        like reference M&G Cobiter 80.    -   b. The polymer material referenced under 1a. is converted on a        classical injection machine, like type Huskey, operated at        typical machine settings:

Extruder Barrel 270-290° C. Nozzle 270-290° C. Manifold 275-295° C.Gates 280-300° C. Mold Cooling Water 10-15° C. Cycle Time 10-60 seconds

-   -   c. Position 1b is repeated with a commercially available grade        of a crystallizable polymer, being PET, with an increased IV        range of 0.82-0.86, like reference M&G Cleartuf Max.    -   d. Position 1b is repeated with a commercially available grade        of a crystallizable co-polymer, being PET based, within a        classical IV range of 0.78-0.82, like reference M&G Cleartuf        8006.

2. Hot Runner System

-   -   a. Positions 1a through 1d are executed with normal classical        hot runner configuration for injected preform production.    -   b. Positions 1a through 1d are repeated with the incorporation        of specific hot runner modifications as referenced under FIGS. 2        through 9.

3. Injection Preform

-   -   a. Positions described under 1 and 2 are executed with the use        of an industry available preform suitable for an injection        stretch blow molded bottle of a selected volume size.    -   b. Position 3a is repeated but with the use of an industry        available preform suitable for an injection stretch blow molded        bottle, the preform having a reduced axial stretch ratio for the        selected volume size.    -   c. Position 3a is repeated with adapted preform mold        temperatures in-between 8 and 60° C. for either neck and/or body        area.    -   d. Position 3b is repeated with adapted preform mold        temperatures in-between 8 and 60° C. for either neck and/or body        area.

4. Preform Reheating Process

-   -   a. The preforms obtained from positions 3a through 3d are        reheated on an conventional blow molding machine, like Sidel,        operated under preform reheat temperature range of 90 to 95° C.    -   b. The performs obtained from positions 3a through 3d are        reheated on an conventional blow molding machine, like Sidel,        operated under preform reheat temperature range of 100 to 110°        C.    -   c. The performs obtained from positions 3a through 3d are        reheated on an conventional blow molding machine, like Sidel,        operated under preform reheat temperature range of 120 to 130°        C.

5. Blow Molding Process

-   -   a. The performs obtained from positions 4a through 4c are blown        in a conventional blow mold suitable for an injection stretch        blow molded bottle of the selected size operated at mold        temperature of 23° C.    -   b. The performs obtained from positions 4a through 4c are blown        in a conventional blow mold suitable for an injection stretch        blow molded bottle of the selected size operated at mold        temperature of 80° C.    -   c. The performs obtained from positions 4a through 4c are blown        in a conventional heat set blow mold suitable for an injection        stretch blow molded bottle of the selected size operated at mold        temperature of 160° C.

The above example demonstrate the benefits as set out in the descriptionwith respect to end functional properties including improvements onmechanical strength, barrier performance, dimensional stability andoptimized wall thickness about 0.2 mm of the resulting stretch blowncontainer as the general injection and blow molding processing output.The resulting containers are ideally used for hot fill applications(with shrinkage percentage being less than about 4%) and for diversecarbonated and/or non-carbonated beverage applications.

In the specification and the figures only typical embodiments have beendisclosed. Specific terms have been used in a generic and descriptivesense and done not for the purpose of limitation. As apparent to thoseskilled in the art, it should be understood that this invention is notto be unduly limited to the illustrative example as set out hereinabove.

1. An injection blow molding method for making a container comprisingthe steps of injecting a molten crystallizable polymer in a preform moldvia a hot runner system and biaxially stretching the preform by blowingto form a container, wherein the preform comprises regular or irregularsequence of variations in molecular pre-alignment/orientation betweendifferent locations of the cross-section of the preform.
 2. An injectionblow molding method for making a container comprising the steps ofinjecting a molten crystallizable polymer in a preform mold via a hotrunner system and biaxially stretching the preform by blowing to form acontainer, wherein the preform comprises regular or irregular sequenceof variations in molecular pre-alignment/orientation and regular orirregular sequence of variations in crystallinity between differentlocations of the cross-section of the preform.
 3. An injection blowmolding method for making a container comprising the steps of injectinga molten crystallizable polymer in a preform mold via a hot runnersystem and biaxially stretching the preform by blowing to form acontainer, comprising selectively modifying the flow path of the moltencrystallizable polymer within the hot runner system.
 4. An injectionblow molding method for making a container comprising the steps ofinjecting a molten crystallizable polymer in a preform mold via a hotrunner system and biaxially stretching the preform by blowing to form acontainer, wherein the container comprises regular or irregular sequenceof variations in molecular pre-alignment/orientation and regular orirregular sequence of variations in crystallinity between differentlocations of the cross-section of the container.
 5. The method accordingto claim 1, wherein in the hot runner system the polymer melt flow pathcomprises profiling within the needle, within the bus or combinationsthereof.
 6. The method according to claim 1, wherein, for the polymermelt flow path, inserts are placed in the hot runner system.
 7. Themethod according to claim 2, wherein the injection molding cavity isprovided with cooling provisions to influence the regular or irregularsequence of variations in molecular pre-alignment/orientation andvariations in crystallinity between different locations of thecross-section of the preform.
 8. The method according to claim 1,wherein the crystallizable polymer is PET, high IV PET or modified PETor a combination thereof.
 9. The method according to claim 8, furthercomprising the step of providing as copolymers suitable for modifyingthe preform's physical characteristics polyamide, PGA, PEN, or mixturesthereof.
 10. The method according to claim 8, further comprising thestep of providing as additives to the polymer, anti-oxidants,UV-absorbers, dyes, colorants, nucleating agents, fillers or mixturesthereof.
 11. The preform suitable for blow molding made out ofcrystallizable polymers, wherein the preform comprises regular orirregular sequence of variations in molecular pre-alignment/orientation.12. The preform suitable for blow molding made out of crystallizablepolymers, wherein the perform comprises regular or irregular sequence ofvariations in molecular pre-alignment/orientation and regular orirregular sequence of variations in crystallinity between differentlocations of the cross-section of the preform.
 13. The preform accordingto claim 11, wherein the crystallizable polymer is PET, high IV PET ormodified PET or a combination thereof.
 14. The preform according toclaim 13, comprising, as copolymers suitable for modifying thecontainer's physical characteristics polyamide, PGA, PEN, or mixturesthereof.
 15. The preform according to claim 13, comprising, as additivesto the polymer, anti-oxidants, UV-absorbers, dyes, colorants, nucleatingagents, fillers and mixtures thereof.
 16. A container made by blowmolding out of crystallizable polymers comprising a regular or irregularsequence of variations in molecular pre-alignment/orientation andregular or irregular sequence of variations in crystallinity betweendifferent locations of the cross-section of the container.
 17. Thecontainer according to claim 16, wherein the crystallizable polymer isPET, high IV PET or modified PET or a combination thereof.
 18. Acontainer according to claim 17, including, as copolymers for modifyingthe container's physical characteristics, polyamide, PGA, PEN, ormixtures thereof.
 19. The container according to claim 17, furthercomprising, as additives, anti-oxidants, UV-absorbers, dyes, colorants,nucleating agents, fillers or mixtures thereof.
 20. The containeraccording to claim 16, the shrinkage percentage of said container duringhot fill operations being less than about 4%.
 21. The containeraccording to claim 16, having parts with wall thickness less than about1 mm.
 22. Use of a container as defined in accordance with claim 16 forhot-fill applications.
 23. Use of a container as defined in accordancewith claim 16 for carbonated or non-carbonated beverage applications.